Mechanical Engineering
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Item ENERGY ANALYSIS OF A METRO TRANSIT SYSTEM FOR SUSTAINABILITY AND EFFICIENCY IMPROVEMENT(2023) Higgins, Jordan Andrew; Ohadi, Michael; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The industrial sector in the US accounted for 33% of the overall energy consumption and 23% of total GHG Emissions in 2022, necessitating the need for energy efficiency and decarbonization of this sector. This study identifies common opportunities and challenges while performing energy audits for the State of Maryland public transportation maintenance complex and proposes site-specific energy efficiency measures. Utilizing performance indices such as Energy Use Intensity (EUI) and load factor from end-use energy data, as well as walkthrough observations from energy audits, energy efficiency measures specific to each facility were formulated to augment the overall energy performance. Additionally, energy modeling helped pinpoint the additional scope of energy efficiency improvements that could have potential significant energy performance improvements and reduce on-site GHG emissions. Among the energy conservation measures considered, the re-sizing and decarbonization of HVAC equipment has the greatest contribution to energy and GHG savings, with a 100% decrease in natural gas, a 37% decrease in electricity use annually, and net decrease of 272 Mton CO2. This study aims to highlight the similarities and differences in existing transportation and maintenance facilities and the applicable technology(ies) that could streamline and serve as a guide for energy audits for transportation maintenance facilities by demonstrating the most common energy efficiency measures and subsequent achievable savings for these facilities.Item DETERMINING MEASUREMENT REQUIREMENTS FOR WHOLE BUILDING ENERGY MODEL CALIBRATION(2020) Dahlhausen, Matthew Galen; Srebric, Jelena; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Energy retrofits of existing buildings reduce grid requirements for new generation and reduce greenhouse gas emissions. However, it is difficult to estimate energy savings, both at the individual building and entire building stock level, because building energy models are poorly calibrated to actual building performance. This uncertainty has made it difficult to prioritize research and development and incentive programs for building technologies at the utility, state, and federal level. This research seeks to make it easier to generate building energy models for existing buildings, and to calibrate buildings at the stock level, to create accurate commercial building load forecasts. Once calibrated, these building models can be used as seeds to other building energy model calibration approaches and to help utility, state, and federal actors to identify promising energy saving technologies in commercial buildings. This research details the economics of a building energy retrofit at a singular building; contributes significantly to the development of ComStock, a model of the commercial building stock in the U.S.; identifies important parameters for calibrating ComStock; and calibrates ComStock for an example utility region of Fort Collins, CO against individual commercial building interval data. A study of retrofit costs finds that measure cost and model uncertainty are the most significant sources of variation in retrofit financial performance, followed financing cost. A wide range of greenhouse gas pricing scenarios show they have little impact on the financial performance of whole building retrofits. A sensitivity analysis of ComStock model inputs across an exhaustive range of models identifies 19 parameters that explain 80 of energy use and 25 parameters that explain 90% of energy use. Building floor area alone explains 41% of energy use. Finally, a comparison of ComStock to Fort Collins, CO interval meter data shows a 6.92% normalized mean bias error and a 16.55% coefficient of variation of root mean square error based on normalized annual energy per floor area. Improvements in meter classification and ComStock model variability will further improve model fit and provide an accurate means of modeling the commercial building stock.Item CO2 TRANSCRITICAL REFRIGERATION WITH MECHANICAL SUBCOOLING: ENERGY EFFICIENCY, DEMAND RESPONSE AND THERMAL STORAGE(2018) Bush, John; Radermacher, Reinhard; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation examines two important concepts: improvements to transcritical carbon dioxide (CO2) refrigeration systems being deployed in supermarkets, and their potential use for demand response and load shifting in a utility-connected application. As regulatory pressure increases to reduce the use of ozone depleting and greenhouse gases as refrigerants, the heating, ventilation, air conditioning and refrigeration (HVAC&R) industry is moving towards alternative refrigerants including natural substances such as carbon dioxide. CO2 has already gained traction as the refrigerant of choice for supermarket applications in some countries, but deployment in warmer climates has been slower due to concerns over efficiency when the cycle operates in transcritical mode. Among the cycle enhancements considered to overcome these concerns is the use of dedicated mechanical subcooling. Laboratory testing was performed on a transcritical booster system with mechanical subcooling to quantify the system performance with and without the subcooler. Data was used to develop and validate transient models, which in turn were used to study the system-wide effects of demand response, particularly short-term shedding of medium or low temperature load. Systems can provide value to the electric grid if they can be responsive to changes in electric utility generation, as indicated by direct calls to shed load or price signals. To further expand the potential usefulness of the refrigeration cycle in grid-interactive operation, the integration of thermal storage is considered. In particular, the integration of thermal storage into the subcooling system is investigated. The mechanical subcooler is used to “charge” a storage media (such as water or another phase change material) overnight, and the storage media allows the subcooler to turn off during peak hours. This allows the system to shift load and allow temporary reduction in electric power usage without a reduction in delivered refrigerating capacity. These two paths are potentially complementary: the load shifting of the integrated thermal storage provides long-term load reduction, while direct load shedding in evaporators allows more agile, short-term reductions. The models developed and validated with laboratory data and expanded upon with thermal energy storage and demand response approaches provide new learnings into enhanced load shifting and demand response capability. The findings of this work show that particularly in time-of-use rate structures with a high ratio of on-peak to off-peak pricing, the thermal storage and load shedding strategies here can provide a reduction in total refrigerating energy cost, even though the changes proposed introduce a slight increase in daily energy under the simulated conditions. In a simulated hot day for Baltimore, Maryland, the energy consumption was 2.6% higher using the thermal storage system than without. In the most extreme case, comparing an aggressive real-world Time-of-Use rate with thermal storage and load shedding against a flat-rate case from the same utility and no controls or storage, a cost savings reduction of 21% was calculated. Comparing baseline operation against a controlled load-shifting strategy under the same time-of-use rate plan, the cost reduction was in the range of 2.8-8.7% depending upon the specific plan.Item SIMULATION AND ANALYSIS OF ENERGY CONSUMPTION FOR TWO COMPLEX AND ENERGY-INTENSIVE BUILDINGS ON UMD CAMPUS(2017) Savage, Dana Mason; Ohadi, Michael M; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Microbiology Building and Hornbake Library are two multi-purpose and complex buildings, and are among the highest energy-intensive buildings on the University of Maryland College Park Campus. This thesis details the energy analysis and energy consumption models developed to identify energy savings opportunities for these two buildings. Three reports are given per building: one – a comprehensive summarization of relevant building information; two – a utility analysis, including an energy benchmarking study, evaluating the relative performance of each facility; three – a detailed energy model to replicate current operation and simulate potential energy savings resulting from no-and-low cost energy conservation measures. In total, 11 of the 12 measures simulated are strongly recommended for implementation. The predicted combined energy and utility savings are respectively 18,648.4 MMBtu and $436,128 annually. These actionable proposals to substantially reduce the buildings’ energy consumption contribute to the University’s commitment to achieve greater energy efficiency throughout campus.Item COMPARISON OF WASTE HEAT DRIVEN AND ELECTRICALLY DRIVEN COOLING SYSTEMS FOR A HIGH AMBIENT TEMPERATURE, OFF-GRID APPLICATION(2012) Horvath, Christopher Philip; Radermacher, Reinhard; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Forward army bases in off-grid locations with high temperatures require power and cooling capacity. Each gallon of fuel providing electrical power passes through a complex network, introducing issues of safety and reliability if this network is interrupted. Instead of using an engine and an electrically powered cooling system, a more efficient combined heat and power (CHP) configuration with a smaller engine and LiBr/Water absorption system (AS) powered by waste heat could be used. These two configurations were simulated in both steady state and transient conditions, in ambient temperatures up to 52°C, providing up to 3 kW of non-cooling electricity, and 5.3 kW of cooling. Unlike conventional AS's which crystallize at high temperatures and use bulky cooling towers, the proposed AS's avoid crystallization and have air-cooled HXs for portability. For the hottest transient week, the results showed fuel savings of 34-37%, weight reduction of 11-19%, and a volumetric footprint 3-10% smaller.Item SIMULATION OF ABSORPTION CYCLES FOR INTEGRATION INTO REFINING PROCESSES(2009) Somers, Christopher Michael; Radermacher, Reinhard; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The oil and gas industry is an immense energy consumer. Absorption chillers can be used to recover liquid natural gas (LNG) plant waste heat to provide cooling, which is especially valuable in the oil and gas industry and would also improve energy efficiency. This thesis details the modeling procedure for single and double effect water/lithium bromide and single effect ammonia/water chillers. Comparison of these models to published modeling results and experimental data shows acceptable agreement, within 5% for the water/lithium bromide models and within 7% for the ammonia/water model. Additionally, each model was integrated with a gas turbine as a waste heat source and parametric studies were conducted for a range of part load conditions, evaporator temperatures, and ambient conditions. Finally, the best chiller design was selected among the three evaluated here, and an annual performance study was conducted to quantify the expected cooling performance and related energy savings.